Eleven-year-old Hecate loves being a student at Hexwitch School but gets nervous about things that could go wrong. To try and stem her anxious feelings, she gathers all the facts about different situations--that way, she will always be prepared if disaster strikes.

After stumbling into a pet cemetery, Hecate meets Melinoe, who calls herself a ghost herder. She is in charge of leading the ghosts of pets and other animals to the River Styx in the Underworld. But Melinoe doesn't notice when one of her ghost animals follows Hecate home! More and more of the lost ghosts gather with Hecate, and she learns they have unfinished business left on Earth and refuse to enter the Underworld.

The deceased pets are counting on Hecate, but Melinoe isn't too thrilled with having competition! Can Hecate help the animals without making a new enemy?